The present invention relates to a magnetic object detecting system for an automated guided vehicle system (AGVS) in which at least one mobile vehicle is guided along a traffic path.
AGVS's have been used in many fields of industry. For example, automated guided vehicles are used in transporting semiconductor wafers within factories in the semiconductor industry.
In AGVS, a magnetic strip of magnetic material such as iron ferrite is installed to form a guide lane, and a detection system for detecting the strip is provided to a vehicle to be guided. Thus, the vehicle moves along the magnetic strip by detecting the magnetic strip. The above detection system is usually comprised of a magnetic-field generating coil and a pair of magnetic-field detection coils. When the vehicle is moving along the magnetic strip, both of the magnetic-field detection coils generate relatively large voltage outputs, and when the vehicle does not trace the magnetic strip, at least one of the pair of detection coils produces a small voltage output. These outputs from the pair of detection coils are applied to a steering system of the vehicle and the steering system moves the vehicle so as to make the voltage outputs of the pair of detection coils. Heretofore, the above magnetic-field generating coil is of an air core type and hence the magnetic field generated by the magnetic-field generating coil is distributed broadly over both sides of the generating coil. Therefore, the generating coil produces a magnetic-field not only in the space under the coil but also in the space over the coil. Accordingly, in the case where some magnetic material such as iron as steel is present over the magnetic strip, the detection system erroneously recognizes such magnetic material as the magnetic strip, resulting in malfunction.
Furthermore, a magnetic field generated by the aircore type magnetic-field generating coil spreads over a broad area and change in intensity of the magnetic field is very gradual. Therefore, the detection coils are required to have high sensitivity. This means that the pair of detection coils must be large in size.
As described, the prior art detection system has been limited in detection sensitivity and inevitably large in size.